RFID systems serve for the identification of objects and products and are used inter alfa to automate logistical movements. RFID transponders fastened to the products are read out at an identification point, above all on a change of the owner of the product or on a change of the transport means, and information is optionally written back into the transponder. This results in fast and traceable logistical movements. The detected information is used to control the forwarding, storage, and sorting of goods and products.
The RFID transponders are excited by electromagnetic radiation of the read/write system, also called an interrogator, for radiating the stored information, wherein passive transponders draw the required energy from the transmission energy of the reading system and the less customary active transponders have their own supply for this purpose. Passive transponders are read in accordance with the backscatter method in the established ultrahigh frequency standard EPC Generation 2 UHF RFID, whose air interface is defined in ISO 180000-6, mainly looked at here.
Singulation is a challenge in RFID communications. What is meant by this is that a simultaneous transmission of a plurality of transponders should be avoided to avoid interference and incorrect associations. The singulation should above all take place very simply and without any coordination effort on the side of the transponders since only very limited calculation resources are available there and since the time window of the contact would also be too short for a complex synchronization in many applications.
The anti-collision process defined in ISO 18000-6 in principle also makes possible singulation for transponders of identical content. Each transponder is first addressed individually and independently of its content in the so-called inventory and is asked to communicate. In broad strokes, the time duration of the inventory, also called a round, is divided into 2Q-1 slots. Q is a parameter that the interrogator sets such that in view of an expected or known number of transponders in the reading field the probability of a random collision is small without losing all too much response time through empty slots in so doing.
Each transponder in reading range now generates a random number using the Q parameter. The transponder only responds in the slot thereby fixed during the inventory and is otherwise silent so as not to interfere with the communication between the interrogator and other transponders. The transponder can inter alia communicate its unique identification parameter (UII—unique identification identifier also referred to as a unique item identifier) to the interrogator in its fixed slot. After completion of the inventory, the interrogator thus knows all the transponders with which communication is possible. Since the transponders fix their slots randomly independently of one another, collisions are not precluded. The interrogator must recognize this and must start a new inventory, where necessary with a different Q.
The interrogator can also obtain deeper access to the transponder in the course of an inventory, i.e. can communicate and execute an access command. In this respect, a transponder having a specific UII is looked for as a rule. As soon as a transponder with the sought UII therefore responds in a slot of the access inventory, a handle is requested, the command is transmitted to the transponder with this handle, is executed there and is acknowledged.
This procedure starts from the basis that the UII is actually only allocated once within the total transponder population so as never to locate two transponders having the same UII simultaneously in the reading field. The access command would otherwise be executed by all the transponders that satisfy the condition within the inventory, namely here having the same UII. The number of transponders participating in an inventory can admittedly be narrowed down by filters transmitted to the transponders beforehand. Identical UIIs would, however, also not prevent a simultaneous participation in the context of such filters. The inventory would in the best scenario, depending on the implementation in the interrogator, still recognize that a UII has been awarded a multiple of times, but would subsequently no longer be able to distinguish or separately address the associated transponders.
It is, however, unlike with RF transponders, actually the responsibility of the operator to provide this uniqueness of the UIIs. As a rule, a stack or a roll of transponders having identically pre-programmed UIIs are delivered and an initial writing with different UIIs is therefore required before the actual operation.
The known singulation is therefore not suitable to initially assign a UII to a specific transponder and to store it there for further operation. Instead, the transponders have to be isolated in a geometrically physical manner so that communication takes place with exactly the desired transponder by corresponding structures and a targeted choice of the transmission parameters of the interrogator. Some conceivable measures for this are a distance that is as small as possible between the interrogator and the transponder, a reduction of the transmission power to the smallest possible degree, construction measures that shadow other transponders or a suitable linear polarization. In addition, a SELECT mask can be set for the UII of the manufacturer set ex works, said mask, however, only separating the totality of the new transponders from possible further transponders. All this is complex and also not even possible in every situation. If the artificial singulation fails, all the transponders accidentally also addressed receive the write command to the UII and then have the same new UII among one another in the future.
An initial content should frequently also be written to the transponder with the UII, with this content being predefined as a simple label or in an outer packaging of the transponder, for instance in the form of a text, barcode or 2D code. The association between the transponder and this information must accordingly be secured at exactly this point in time. Otherwise, not only false UIIs would be allocated, but other transponder data would also be compromised.
Some transponder types have a serial number programmed by the manufacturer in a different memory sector than that for the UII. This would then allow a singulation with the aid of SELECT masks and the initial UII could also be assigned in this manner. This is a comparatively time-consuming operation, particularly since the serial numbers must first also still be read from the transponders. Transponders having pre-programmed serial numbers are also more of an exception so that this approach is at best a part solution.
A not insubstantial effort has to be made overall for the unambiguous association of a command to a specific known transponder. The UII initialization is associated with expensive designs and is only possible with a restricted pulsing. This will frequently not be possible “on the object”, but rather requires an additional manual process, for example using a hand-held device.